1. Field of the Invention
The present invention relates to a substrate processing system formed by incorporating a processing unit for improving the surface condition of a resist film formed on a substrate into a coating and developing system for processing a substrate, such as a semiconductor wafer.
2. Description of the Related Art
Usually, a photolithographic process among those for fabricating a semiconductor device includes, a resist film forming process for forming a resist film on a base film formed on, for example, a semiconductor wafer (hereinafter, referred to simply as “wafer”) by applying a resist solution to the wafer, an exposure process for exposing the resist film through a mask provided with a circuit pattern to light to form a latent circuit pattern in the resist film, a developing process for processing the exposed resist film by a developer to form a resist pattern, and an etching process for etching the base film formed on the wafer by using the resist pattern as a mask.
A plurality of vertical and horizontal ridges and furrows are formed in the side surfaces of a resist pattern formed by the developing process due to the wave characteristic of the light used for irradiating the surface of the wafer by the exposure process. For example, the wavelengths of KrF light and ArF light are 248 nm and 193 nm, respectively. Those ridges and furrows are LWR lines (line width roughness lines) and LER lines (line edge roughness lines). When the resist pattern having surfaces roughened by the ridges and furrows are used for etching the base layer by the etching process, ridges and furrows corresponding to those of the resist pattern R are formed in the base film. Consequently, a precise circuit pattern cannot be formed and hence a semiconductor device of a desired quality cannot be produced.
The inventors of the present invention previously proposed a smoothing method (smoothing process) to improve the surface quality of a circuit pattern by smoothing LWR lines and LER lines in JP-A 2005-19969 (Claims and FIGS. 4, 5 and 16).
This smoothing process can smooth the surface of the resist pattern by evening the ridges and furrows formed in the surface of the resist pattern by discharging a solvent vapor onto the surface of the substrate provided with the resist pattern and processed by an exposure process and a developing process to swell the resist pattern.
To carry out the smoothing process, safety measures, such as sealing the smoothing unit, ventilating the processing unit and providing the smoothing unit with explosion-proof measures, need to be taken to prevent the solvent vapor from diffusing in the smoothing unit. An exhaust cup is placed in the smoothing unit to prevent the diffusion of the solvent vapor in the smoothing unit.
However, it is difficult to surely recover the solvent vapor discharged through the nozzle only by the exhaust cup and it is possible that the solvent vapor leaks into the smoothing unit. Therefore, the solvent vapor leaks out of the smoothing unit to contaminate the coating and developing system and the exposure system when the smoothing unit is incorporated into a coating and developing system. If the solvent vapor leaks outside, it is possible that the leaked solvent vapor gives detrimental effects to the human body.